Chapter 10 Nuclear Chemistry (P. 290)

Nuclear Chemistry Notes Chapter 10 Nuclear Chemistry (p. 290)

Radioactivity- the process in which an unstable atomic nucleus emits (or sends out) charged particles and energy . Charged particles and various types of energy can escape from all nuclei with atomic numbers of 84 or higher (i.e. Polonium through rest of periodic table) . Will spontaneously change into other isotopes over time; producing other elements . Can’t see, hear, taste, touch or smell radioactivity . Radioactivity can break the bonds holding proteins and DNA together causing the cells to no longer function correctly . Used to kill cancer cells Nuclear decay – atoms of one element can change into atoms of a different element altogether (i.e. uranium-238 decays into thorium-234) Nuclear radiation – charged particles and energy that are emitted from the nuclei of radioisotopes

Types of Nuclear Decay (p. 293) Common types of nuclear radiation include: alpha particles, beta particles, and gamma rays Alpha decay – release of alpha particles during radioactive decay  An alpha particle is positively charged particle made up of 2 protons and 2 neutrons (the same as a Helium nucleus)  Result = change the radioactive nucleus into one of a different element with an atomic number decreased by 2 and a mass number decreased by 4  For example: Po  Pb + He  Largest and slowest form  Least penetrating; a sheet of paper can stop them Beta decay- occurs when a radioactive nucleus releases a high-speed electron . Beta particles are electrons . More penetrating than alpha particles . Stopped by sheet of aluminum foil . The result is to increase the original atomic number by one, but leave the mass number of the new nucleus unchanged . For example: Technetium-98 is converted into Ruthenium-98 . Tc  Ru + e Gamma rays- strong electromagnetic waves with very high frequency and energy . Penetrating rays; not particles . Most penetrating; dangerous to us . No mass, no charge . Travel at the speed of light . Several centimeters of lead or several meters of concrete are required to stop these rays Chapter 10.2 Rates of Nuclear Decay (p. 298)

Half-life: time required for half of the original substance to decay; rates are constant for a given radioisotope Polonium-214= less than a thousandth of a second Uranium-238 = 4.5 billion years . Disposal of used nuclear materials must be studied from the standpoint of the time needed for radioactive products to convert into stable nuclei Calculating Half-life (p. 300): Iridium-182 has a half-life of 15 minutes. If you start with 1 gram of Iridium-182, how much is left after 45 minutes? Half-life elapsed = Total time of decay Half-life = 45 minutes = 3 half-lives elapsed 15 minutes ½ x ½ x ½ = 1/8 1 gram x 1/8 = 0.125 grams of Iridium would remain

Questions: 1. If you start with 1 gram of Radon-222 (half- life of ~ 4 days), how much would remain after 8 days?

2. If you start with 5 grams of Iodine-131 (half- life of 8 days), how much would remain after 32 days?

Carbon dating- using Carbon-14 (half-life of 5730 years) to date fossils . Plants take in C-14 as they respire (in CO2) . All living things have a somewhat constant amount of C-14 . When an organism dies, its C-14 decays without replacement . By measuring the amount of C-14 remaining in a fossil or skeleton, scientists can determine the approximate age of the material . Only remains within the last 50,000 years have enough C-14 left to measure

Chapter 10.4 Fission and Fusion (p. 308) Nuclear fission- the splitting of an atomic nucleus into fragments whose combined mass is slightly less than that of the original nucleus . What we call nuclear power . Small loss of mass is converted into large amounts of energy . Only large nuclei with atomic numbers above 90 can undergo nuclear fission . Chain reaction - ongoing series of fissions reactions resulting in release of tremendous amount of energy . In a fission reactor, the splitting is controlled by slowing down the fast-moving neutrons, which are a product of the reaction . U-235 is a commonly used fuel with krypton and barium as products (reactants  products) . Fission bomb (atomic bomb): the result of an uncontrolled fission reaction in which the released neutrons spontaneously support continued reactions . Requires a critical mass (smallest possible mass of a fissionable material that can sustain a chain reaction) of the material but a huge amount of energy is released . First atomic bomb in 1945 – contained 5kg (about 11 lbs) of Plutonium-239 but produced an explosion that was equivalent to 18,600 tons of TNT so thanks to Logan Galloway…. That’s 1 lb Pu to 409,200,000 lbs TNT Nuclear fusion- combining of two nuclei to form one nucleus of slightly less total mass . Again, the missing mass is converted into large amount of energy . Difficult to induce because extremely high temperatures are required (such as found on the sun) . Reaction that powers the sun can be broken down into the combining of four hydrogen nuclei into one helium nucleus, two electrons and energy . Scientists have not found a way to make fusion reactors successful on a large scale . If they could, fusion could supply our energy needs using low-cost available fuel with fewer environmental problems than fossil fuels (coal, oil) combustion or fission . Hydrogen is the most abundant element in the universe . Hydrogen bombs (fusion powered) have been developed but require a fission bomb to be exploded within a sample of a hydrogen isotope to trigger the fusion reaction

Nuclear Energy Nuclear reactor- uses the energy from a controlled nuclear fission chain reaction to generate electricity . Most have fuel, control rods and cooling systems, core (where the actual fission takes place) . Neutrons being absorbed by U-235 . Undergoes fission and releases more neutrons; reactions continues . Rods containing boron or cadmium are used to absorb some of the neutrons and slow reaction . Energy released at a constant rate . Produces electricity . Produces about 20% of the electricity in the US Pros- . Less harmful to environment than the use of fossil fuels . Produces no air pollution . Doesn’t produce CO2 . Doesn’t contribute to global warming Cons- . Mining of uranium and extraction of U-235 does cause environmental damage . Water circulated around the core has to be cooled before sent back into environment . Possible escape of harmful radiation from power plants (Chernobyl; Three Mile Island) . Storage of used fuel rods while they decay . Disposal of reactor itself when it no longer runs as it should

Nuclear wastes-radioactive by-products that result when radioactive materials are used

Using fusion power one day??? . Now we can’t use because of the high temperatures needed . Fusing the nuclei in 1 g of heavy hydrogen gives off about the same amount of energy as burning more than 8 million grams of coal . Hydrogen nuclei source of energy for nuclear fusion; abundant . By-products not radioactive . Helium is the main by-product

Summary: Radiation Symbol Particles Electric Energy Energy Decay charge stopped by Alpha α 2 protons, 2 Positive Low A piece of ↓mass, neutrons paper ↓# (He) Beta β 1 electron Negative Medium Aluminum Mass no foil change, ↑# Gamma γ Wave of Neutral High Thick energy lead /concrete https://www.youtube.com/watch? v=wsspFQn0mWM Fission : splits large nucleus, used in nuclear power Fusion: fuses two small nuclei Nuclear power: Pro: no air pollution, used in medicine Con: nuclear waste storage

Nuclear Fission Nuclear Fusion

Chain Reaction Samples: 1. Which best represents a negative consequence of using nuclear power technology? a. nuclear reactions are less efficient than other types of exothermic reactions. b. the estimated supply of uranium will fuel nuclear reactors for less than 100 years. c. steam from nuclear reactors may accumulate in the environment and disturb the water cycle d. radioactive waste from reactors is toxic and must be stored safely for thousands of years. 2. In what way are fission and fusion reactors similar? a. both reactions transform mass into energy b. the same temperatures and pressures get them started c. both reactions involve the combining of atomic nuclei d. both reactions are endothermic

3. Which high frequency, short wavelength electromagnetic rays have no charge and can penetrate 2 to 3 cm of lead? a. alpha rays b. beta rays c. gamma rays d. light rays

4. What is the term that describes a doubly-charged helium nucleus containing two protons and two neutrons? a. alpha particle b. beta particle c. gamma particle d. light particle

5. Describe the reaction illustrated by: 3H + 2H → 4 2He + 1n a. spontaneous fission b. induced fission c. decay d. fusion 6. Uranium-238 has 92 protons and 146 neutrons. It undergoes radioactive decay by emitting an alpha particle. What element is the product of this decay? a. an isotope of uranium having 92 protons and 144 neutrons. b. an ion of uranium having 92 protons and 91 electrons c. the element of neptunium, which has 93 protons and 144 neutrons d. the element thorium, which has 90 protons and 144 neutrons.

7. Select the product of radioactive decay that has the greatest ability to penetrate matter. a. alpha particles b. beta particles c. gamma rays d. neutrons

8. Fusion describes the process of a. two small atoms joining together to produce one larger atom b. several small atoms joining together to produce one or more larger atoms c. several small atoms joining together to form a macromolecule d. two large atoms breaking apart to form smaller atoms

9. Which two particles have approximately the same mass? a. proton & electron b. proton & neutron c. neutron & alpha particle d. electron & alpha particle